Implantable intravenous cardiac stimulation system with pulse generator housing serving as optional additional electrode

ABSTRACT

Described is an implantable pulse generator housing for enclosing and containing pulse generator circuitry. The housing is formed of electrically conductive metal defining an electrically conductive outer surface which may be connected to the pulse generator circuitry for delivering electrical energy to the heart. A programmable switch operable by the pulse generator circuitry is provided to discharge electrical pulses between selected electrodes and the conductive pulse generator housing in accordance with whether a first or second cardiac condition is detected.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.09/884,862, filed on Jun. 19, 2001, which is a continuation of U.S.patent application Ser. No. 09/689,018, filed on Oct. 12, 2000, nowissued as U.S. Pat. No. 6,280,462, which is a continuation of U.S.patent application Ser. No. 09/344,843, filed on Jun. 28, 1999, now U.S.Pat. No. 6,157,860, which is a continuation of U.S. patent applicationSer. No. 08/964,120, filed Nov. 4, 1997, now U.S. Pat. No. 5,916,238,which is a continuation of U.S. patent application Ser. No. 08/380,538,filed on Jan. 30, 1995, now U.S. Pat. No. 5,713,926, which is acontinuation of U.S. patent application Ser. No. 07/917,899, filed Jul.24, 1992, now U.S. Pat. No. 5,385,574, which is a continuation-in-partof U.S. patent application Ser. No. 07/514,251, filed on Apr. 25, 1990,now U.S. Pat. No. 5,133,353, the specifications of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to an implantable cardiac stimulation lead andelectrode system for applying electrical energy to an abnormallyfunctioning heart and more particularly to an implantable pulsegenerator housing having electrically conductive walls serving as adefibrillation discharge electrode.

Electrodes implanted in the body for electrical stimulation of muscle orbody organs are well known. More specifically, electrodes implanted onor about the heart have been used to reverse certain abnormal andlife-threatening arrhythmias. Electrical energy is applied to the heartvia the electrodes to return the heart to normal sinus rhythm.

Common abnormal cardiac arrhythmias include bradycardia (slower thannormal heartbeat rhythm), ventricular tachycardia (faster than normalheartbeat rhythm), and ventricular fibrillation (sporadic anduncoordinated beating of the heart). The latter two arrhythmiasgenerally are fatal if left untreated.

To control the heartbeat rhythm and prevent fatalities from ventriculartachycardia and fibrillation, several devices have been designed havingthe ability to stimulate the heart according to a sensed cardiac signalsuch as a sensed ECG signal. See for example U.S. Pat. No. 4,603,705 toSpeicher et al. The Speicher et al. patent discloses a multipleelectrode unitary intravascular cardiac catheter having a distalelectrode for sensing and pacing, an intermediate electrode for sensing,pacing and cardioverting, and a proximal electrode for sensing andcardioverting. This multiple electrode catheter maintains the abilityfor heart rate sensing and low threshold pacing immediately followingcardioversion.

There are many types of defibrillation cardioversion electrodes in theart. U.S. Pat. No. 4,825,871 to Cansell discloses adefibrillation/cardioversion shock system in which the box housing thepulse generator circuitry serves as a support for a discharge electrode.Specifically, the metal box is enclosed by a plastics material and ametal plate is attached to the metal box and electrically connectedtherewith. Charges collected by the metal plate are transmitted to themetal box, which serves as a collector. The metal box itself is not usedas an electrode in the Cansell system.

The need therefore exists for implantable cardiac stimulation leadsystem capable of performing standard pacing, such as anti-bradycardiapacing, anti-tachycardia pacing, low-energy cardioversion, andhigh-energy defibrillation.

SUMMARY OF THE INVENTION

It is a primary object of this invention to provide an implantablecardiac stimulation lead system having pacemaking, cardioversion andhigher energy defibrillation capabilities.

It is an additional object of this invention to provide an implantablecardiac stimulation lead system having pacemaking, cardioversion anddefibrillation capabilities via a selectable defibrillation electrodeconfiguration.

It is yet a further object of this invention to provide an implantablecardiac stimulation lead system utilizing a relatively small number ofimplantable parts.

It is still another object of the present invention to provide animplantable pulse generator housing made entirely or partially but in aselective manner, of electrically conductive material, serving as adefibrillation electrode.

It is yet a further object of the invention to provide an electricallyconductive portion of an implantable pulse generator housing which,together with electrical discharge surfaces extending therefrom, serveas an electrode.

It is still another object of the present invention to reduce the sizeof the pulse generator housing by eliminating one terminal on thehousing.

Briefly, the implantable cardiac stimulation lead system of the presentinvention comprises a transvenous endocardial or epicardial lead havinga plurality of electrodes. Typically, the lead electrodes are capable ofsensing and performing standard anti-bradycardia pacing,anti-tachycardia pacing, cardioversion and defibrillation. Thetransvenous lead is connected to a pulse generator having full-functionpacing capabilities as well as cardioversion and defibrillationcapabilities. The housing of the pulse generator (together with, asdesired, electrical discharge surfaces extending therefrom) isconductive and is connected to the pulse generator circuitry so that itmay selectively serve as a discharge electrode. The outer surface of thepulse generator could be of a special configuration to facilitate itsdischarge capabilities. Typically, the pulse generator is implanted inthe pectoral or abdominal region of the body proximate the heart. Aprogrammable switch or other type of circuitry is provided to select theelectrode configuration which may include or exclude the pulse generatorhousing electrode. As a result, different electrode configurations canbe obtained for specific types of cardiac stimulations.

In a first embodiment, the electrode surface of the pulse generatorhousing comprises a portion of the conductive wall of the housing.

In a second embodiment, the electrode surface comprises conductive meshattached to the pulse generator housing.

In a third embodiment, the pulse generator housing is a metal housing,all or selective ones of the surfaces of which, together with, asdesired, electrical discharge surfaces extending therefrom, areconductive.

In accordance with a fourth embodiment, the other surface of theconductive pulse generator housing is platinum.

The fifth embodiment relates to dedicating isolated conductive surfaceregions from one mother, such isolated regions may serve for separatelysensing, pacing and shocking.

In accordance with the sixth embodiment, an insulative mask is disposedover a conductive surface of the pulse generator housing.

In a seventh embodiment, a sensing switch is used to determine when thepulse generator is implanted and when it is outside the body of thepatient.

The above objects and advantages of the present invention can be furtherunderstood when reference is made to the following description, taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating the pulse generator housingserving as a cardiac electrode in accordance with a first embodiment ofthe present invention.

FIG. 2 is a cross-sectional view taken through line 2-2 of FIG. 1.

FIG. 3 is a perspective view illustrating the pulse generator housinghaving conductive mesh on a face thereof for serving as a cardiacelectrode in accordance with the second embodiment of the presentinvention.

FIG. 4 is a cross-sectional view taken through line 4-4 of FIG. 3.

FIG. 5 is a side view of a transvenous electrode and lead used inconjunction with the pulse generator illustrated in FIG. 1 or FIG. 3.

FIG. 6 is a diagram illustrating the placement of the pulse generatorhousing adjacent the heart and connected to the implanted transvenouselectrode and lead.

FIG. 7 is a cross-sectional view of the pulse generator housingaccording to a third embodiment of the present invention.

FIG. 8 is a perspective view of the pulse generator housing according toa fourth embodiment.

FIG. 9 is a cross-sectional view taken through line 9-9 of FIG. 8.

FIG. 10 is a cross-sectional view of a portion of the pulse generatorshousing illustrating a fifth embodiment.

FIG. 11 is a perspective view of the pulse generator housing accordingto a sixth embodiment.

FIG. 12 is a perspective view of the pulse generator housing withextending discharge surfaces according to a seventh embodiment.

FIG. 13 is a perspective view of the pulse generator housing withextending discharge surfaces according to an eighth embodiment.

FIG. 14 is a perspective view of the pulse generator housing withextending discharge surfaces according to a ninth embodiment.

FIG. 15 is a front view of a patient illustrating a dischargeconfiguration including the pulse generator according to the seventhembodiment.

FIG. 16 is a block diagram illustrating the pulse generator.

FIG. 17 is a block diagram showing the programmable switch.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1 and 2, the pulse generator housing of the presentinvention is generally shown at 10. Typically, housing 10 is of arectangular box shape having four side walls, a top wall, and a bottomwall. In one embodiment, at least one of the side walls is highlyconductive. To this end, housing 10 includes side wall 12 having anouter discharge surface 14 formed of highly electrically conductivematerial. The conductive surface 14 is connected to the pulse generatorcircuitry 18 via a programmable switch 16. The pulse generator circuitry18 is insulated from the outer discharge surface and electricallyconnected to electrode lead plug receptacle assembly 20.

As previously mentioned, the number of side walls of housing 10 havingconductive discharged surfaces may vary. However, it is envisioned thatas many as (or more than) four side walls may be made electricallyconductive.

Referring now to FIGS. 3 and 4, a pulse generator housing of a secondembodiment is illustrated at 10′. Housing 10′ is similar to housing 10of FIGS. 1 and 2 except the side wall 12′ includes a conductive meshsurface 14′. It is to be understood that, hereinafter, the term “mesh”includes that as illustrated as well as any other high surface areaconductive materials including microtextured materials. As shown in FIG.4, conductive mesh surface 14′ is electrically connected via switch 16to pulse generator circuitry 18 contained within housing 10′. Inaddition a separate conductive patch (not shown) could be added andconnected to the bottom of the pulse generator housing to increase theconductive surface area. This patch could attach by a snap or othersimilar means to the housing.

The removable pulse generator patch electrode may take several forms.One form may be a subcutaneous array comprised of a helical coil whichencircles the pulse generator housing, and plugs into a terminal or thehousing. Another form may be an array of parallel or radiatingconductive fingers which are funneled subcutaneously proximate the pulsegenerator housing. A clamp may be provided to connect the patchelectrode to the pulse generator housing.

In another embodiment, additional electrical discharge surfaces may beconnected to the pulse generator housing 10. Thus, as illustrated inFIG. 12, a plurality of coiled segment electrodes 14 a, tunnelledsubcutaneously in the patient, may be connected so as to protrude fromand form a contiguous electrical discharge surface with the pulsegenerator housing 10. This additional discharge surface area increasesthe efficiency of the combined coil segments/housing electrode bydecreasing the impedance and increasing the effective electrode surfacearea. This combination has particular application to counter-shocktreatment of tachyarrhythmias. An alternative embodiment is illustratedin FIG. 13, in which a coiled loop 14 b connected to a header 15 anddisposed outside the SQ pocket serves as the additional dischargesurface area. In yet another embodiment, illustrated in FIG. 14, amembrane 14 b, e.g. a silicone rubber layer, is attached to the side ofhousing 10. Coiled segment electrodes 14 a are joined to and protrudefrom membrane 14 b, membrane 14 b both supporting and providingstructural orientation for coiled segment electrodes 14 a. Lead 14 celectrically connects all electrodes 14 a, and is electrically connectedvia plug 14 d to the plug receptacle of pulse generator 10.

FIG. 15 shows a discharge configuration now possible through use of anelectrically conductive pulse generator housing of the presentinvention. In this configuration the pulse generator housing 10 isimplanted so as to function as a pectoral electrode (position C).Discharge paths are possible from an electrode at position RV toelectrodes at positions SVC and C, as well as from electrodes at RV andSVC to electrodes at C and SQ. Further, this configuration may be usedto terminate atrial arrhythmias with shocks given from SVC to C (or,alternatively, from SVC to SQ, or to C and SQ). Similarly, a pectoralelectrode (housing 10) at C may be used for effecting atrialdefibrillation by using a discharge path between an active electrode atRA and the housing position 10 at position C.

The plug receptacle assembly 20 comprises a positive port 22 a and anegative port 22 b. This allows connection of implanted electrodes tothe pulse generator circuitry, so that one electrode may serve as anodeand one electrode may serve as a cathode. If desired, either electrodecould be used in combination with the electrically conductive housing.

A sensor 19 is provided to determine whether the housing 10 is outsidethe body of a patient or inside the body. The purpose of the sensor 19is to prevent a shock from be delivered while the housing is outside thebody and perhaps held in the hand of a physician prior to implant. Thesensor 19 may be a thermal sensor to detect when the housing is at bodytemperature, indicative of being inside the body. The sensor 19 controlsthe switch 16 to permit shocking via the pulse generator housing. Whenthe temperature is other than body temperature, the sensor 19 controlsthe switch 16 so as to prevent discharge via the pulse generator housingby prohibiting connection to the pulse generator circuitry.

Alternatively, the sensor may be embodied as a signal detector to detectsome signal for a period of time before shocking. As a result, a shockmay not be delivered when the unit is outside the body and not sensingsignals from the body.

Pulse generator circuitry 18 has full-function pacing capabilitiesincluding pacing for bradycardia and tachycardia both to inhibit anintrinsic beat or to adapt the rate to a higher or lower rate. Inaddition, circuitry 18 has cardioversion and defibrillation capabilitiesand includes cardiac detection circuitry capable of distinguishing whenthe heart is in normal sinus rhythm, should be paced, or requires higherenergy cardioversion, or defibrillation. The switch 16 is selectivelyactivated to include or exclude the conductive surface(s) of the pulsegenerator housing 10 during the discharge sequence.

Pulse generator housing 10 or 10′ is typically used in conjunction withother cardiac electrodes implanted on or about a human heart. One suchlead is illustrated in FIG. 5. Lead 30 is provided having a catheterportion 31 supporting electrode 28 on the distal end as well aselectrode 29 on a proximate end of catheter portion 31. Lead 30 includesplug connectors 32-34 at its proximal end. In addition, a sensing tipelectrode 36 may be provided at the distal tip of catheter portion 31for sensing cardiac activity. Electrodes 28 and 29 could also havesensing capabilities.

Referring to FIG. 6, in operation, lead 30 is implanted transvenously inthe human heart 38 with electrode 28 in the right ventricle 40 andelectrode 29 proximate the right atrium or the superior vena cava 42.Alternatively, a single catheter electrode may be used for placing theelectrode in the right ventricle. Pulse generator housing 10 or 10′ isimplanted in the pectoral region proximate but not in contact with theheart, just under the skin. Alternatively, the housing 10 or 10′ couldbe implanted in the abdominal region. Plug connectors 32-34 are insertedinto the appropriate ports 22 a, 22 b or 22 c (not shown) of thereceptacle assembly 20. In this implantation position, the electrodesurface of the pulse generator housing may be used in a two electrode orthree electrode configuration, and may replace one of the intravascularcatheter electrodes.

Referring additionally to FIG. 17, when an arrhythmia is sensed where itis appropriate for an electrical pulse to be delivered to the heart 38,the programmable switch 16 determines which electrodes are energizedunder control of circuitry 18. The switch is programmed so that it canselect any combination of three electrodes, such as, for example, anycombination of the right ventricular (RV) electrode 28, pulse generatorelectrode surface 14 and superior vena cava (SVC) electrode 42. Thesuperior vena cava electrode 42 may be replaced by a subcutaneouselectrode. The RV electrode is connected to terminal 22 a and the SVC orsubcutaneous electrode is connected to terminal 22 b. The pulsegenerator conductive surface would be electrically connected in commonwith the SVC or subcutaneous electrode. The switch 16 may be programmedto discharge the RV electrode against the SVC (or subcutaneous)electrode and/or the pulse generator electrode surface(s).

In another possible configuration, if the heart activity is slower orfaster (bradycardia or tachycardia) than normal, the switch 16 istriggered so that the pulse generator circuitry 18 selects onlyelectrode 28 to discharge to the pulse generator housing. On the otherhand, if the sensed activity is indicative of rapid ventriculartachycardia or fibrillation requiring higher energy stimulation, theswitch 16 is triggered so that the pulse generator circuitry 18 selectsboth distal and proximal electrodes 28 and 29, respectively, as well asthe electrode discharge surface 14 to discharge energy from theconductive wall(s) of housing 10 or 10′ for delivering defibrillationelectrical energy to the heart 38.

Also, prior to applying a high energy defibrillating shock to the heart,a lower energy cardioverting shock can be applied between electrodes 28and 29 against the conductive wall(s) of the pulse generator housing 10or 10′. Thereafter, if the heart does not revert back to normal sinusrhythm, the higher energy defibrillation pulse is applied across thesame electrodes.

In yet another alternate form, the programmable switch 16 may beprogrammed to select one of the electrodes 28 and 29, and the conductiveelectrode surface(s) of the pulse generator housing 10 or 10′. In thisway, the electrode discharge surface 14 of the pulse generator housing10 or 10′ will be discharged against only one of the electrodes 28 or29. Further, the choice between the electrodes 28 and 29 may be based oncertain cardiac conditions.

FIG. 7 illustrates a pulse generator housing 50 according to a thirdembodiment. The housing 50 is comprised of a titanium body 52. Theinternal pulse generator circuitry 18 and programmable switch 16 areconnected to the body 52 as described in conjunction with FIG. 2. Theentire outer surface of the body 52 may be conductive or selectivesurface portions may be made insulative. Specifically, as shown in FIGS.8 and 9, an insulative ceramic material 70 may be sputtered (e.g. highenergy plasma deposition) onto the conductive outer surface of the body52. This is useful to create a conductive surface which has a controlledcurrent density, in much the same manner as recently developeddefibrillation cardioversion patch electrodes. See, for example,commonly assigned U.S. Pat. No. 5,063,932. The insulative material maytake the form of a mask or in various patterns known to control currentdensity across a conductive surface. The insulative material may alsotake the form of silicone rubber.

FIG. 10 illustrates a modification to the embodiment of FIG. 7 in whichthe outer surfaces of the body 52 of the pulse generator housing 50 arecoated with platinum 54, a metal which does not anodize, thusmaintaining performance of the housing walls 52 as an anode. Theplatinum surface may be created by sputtering or high energy plasmadeposition and further may be made a microporous surface to minimizekinetic losses (reduce interface impedance).

FIG. 11 illustrates a sixth embodiment in which regions of theconductive surface of the pulse generator housing are dedicated forcertain functions. Specifically, the pulse generator housing 60comprises electrically isolated conductive regions 62, 64 and 66. One ortwo of these regions may be dedicated for sensing purposes while othersmay be dedicated for shocking purposes. Each of these regions isconnected to the pulse generator circuitry 18.

Additionally, a small isolated conductive surface 80 may be created bysputtering a small region of insulative material onto the body 52. Asmall region of conductive material such as platinum may be depositedonto the region 80. The region 82 is electrically connected to the pulsegenerator circuitry through the body 52.

Such a small conductive regional may serve as a return (ground) for apacing configuration, sensing configuration, etc.

Referring to FIG. 16, pulse generator circuitry 18 has full-functionpacing capabilities (pacer 80) including pacing for bradycardia andtachycardia both to inhibit an intrinsic beat or to adapt the rate to ahigher or lower rate. In addition, circuitry 18 has cardioversion anddefibrillation capabilities (cardioverter/defibrillator 82) and includescardiac detection circuitry 84 capable of distinguishing when the heartis in normal sinus rhythm, should be paced, or requires higher energycardioversion, or even higher energy defibrillation. The switch 16 isselectively activated to include or exclude the conductive surface ofside wall 12 from the discharge sequence.

It is considered that the above description is intended by way ofexample only, and is not intended to limit the present invention in anyway except as set forth in the following claims.

1. An apparatus, comprising: a lead having proximal and distalelectrodes for disposition near the heart; an implantable pulsegenerator including pulse generator circuitry for delivering electricalpulses to the heart; wherein the pulse generator circuitry includescardiac detection circuitry for detecting cardiac conditions based uponcardiac rhythm; a conductive pulse generator housing enclosing the pulsegenerator circuitry; a programmable switch operable by the pulsegenerator circuitry to discharge electrical pulses between selected onesof the proximal and distal electrodes and the conductive pulse generatorhousing in accordance with whether a first or second cardiac conditionis detected.
 2. The apparatus of claim 1 wherein the programmable switchis operable to discharge a first type of electrical pulse between theproximal and distal electrodes when a first cardiac condition isdetected and to discharge a second type of electrical pulse between theconductive pulse generator housing and the proximal electrode when asecond cardiac condition is detected.
 3. The apparatus of claim 2wherein the first and second types of electrical pulses are both pacingpulses.
 4. The apparatus of claim 2 wherein the first type of electricalpulse is a pacing pulse and the second type of electrical pulse is adefibrillation pulse.
 5. The apparatus of claim 4 wherein the firstheart condition is bradycardia and the second heart condition isfibrillation.
 6. The apparatus of claim 4 wherein the first heartcondition is tachycardia and the second heart condition is fibrillation.7. The apparatus of claim 1 wherein the programmable switch is operableto discharge a first type of electrical pulse between the proximal anddistal electrodes when a first cardiac condition is detected and todischarge a second type of electrical pulse between the conductive pulsegenerator housing and the distal electrode when a second cardiaccondition is detected.
 8. The apparatus of claim 7 wherein the first andsecond types of electrical pulses are both pacing pulses.
 9. Theapparatus of claim 7 wherein the first type of electrical pulse is apacing pulse and the second type of electrical pulse is a defibrillationpulse.
 10. The apparatus of claim 9 wherein the first heart condition isbradycardia and the second heart condition is fibrillation.
 11. Theapparatus of claim 9 wherein the first heart condition is tachycardiaand the second heart condition is fibrillation
 12. The apparatus ofclaim 1 wherein the programmable switch is operable to discharge a firsttype of electrical pulse between the proximal and distal electrodes whena first cardiac condition is detected and to discharge a second type ofelectrical pulse between the conductive pulse generator housing and theproximal and distal electrodes connected in common when a second cardiaccondition is detected.
 13. The apparatus of claim 12 wherein the firstand second types of electrical pulses are both pacing pulses.
 14. Theapparatus of claim 12 wherein the first type of electrical pulse is apacing pulse and the second type of electrical pulse is a defibrillationpulse.
 15. The apparatus of claim 14 wherein the first heart conditionis bradycardia and the second heart condition is fibrillation.
 16. Theapparatus of claim 14 wherein the first heart condition is tachycardiaand the second heart condition is fibrillation.
 17. A method comprising:sensing cardiac activity in order to detect a first or second cardiaccondition; and, operating a programmable switch so that an electricalpulse is delivered between selected ones of a first electrode, a secondelectrode, and a conductive housing enclosing pulse generator circuitryin accordance with whether a first or second cardiac condition isdetected.
 18. The method of claim 17 further comprising operating theprogrammable switch to discharge a first type of electrical pulsebetween the first and second electrodes when a first cardiac conditionis detected and to discharge a second type of electrical pulse betweenthe conductive pulse generator housing and the first electrode when asecond cardiac condition is detected.
 19. The method of claim 18 whereinthe first and second types of electrical pulses are both pacing pulses.20. The method of claim 18 wherein the first type of electrical pulse isa pacing pulse and the second type of electrical pulse is adefibrillation pulse.